<button id="decrement">-</button>
<span id="count">0</span>
<button id="increment">+</button>
<script src="https://unpkg.com/redux@latest/dist/redux.min.js"></script>

<script>
  // 定义reducer函数 
  // 内部主要的工作是根据不同的action 返回不同的state
  function counterReducer (state = { count: 0 }, action) {
    switch (action.type) {
      case 'INCREMENT':
        return { count: state.count + 1 }
      case 'DECREMENT':
        return { count: state.count - 1 }
      default:
        return state
    }
  }
  // 使用reducer函数生成store实例
  const store = Redux.createStore(counterReducer)

  // 订阅数据变化
  store.subscribe(() => {
    console.log(store.getState())
    document.getElementById('count').innerText = store.getState().count

  })
  // 增
  const inBtn = document.getElementById('increment')
  inBtn.addEventListener('click', () => {
    store.dispatch({
      type: 'INCREMENT'
    })
  })
  // 减
  const dBtn = document.getElementById('decrement')
  dBtn.addEventListener('click', () => {
    store.dispatch({
      type: 'DECREMENT'
    })
  })
</script>